Study On Seismic Performance Of Complex Joints In Track Bearing Layer Of High-Speed Railway Station Building

With the rapid development of railway stations,the high-speed railway station buildings in the form of bridge-station combined structure appear accordingly.The track bearing layer in the high-speed railway station building is subjected to complex force,and its structural form mainly is concrete filled steel tubular(steel reinforced concrete)column-prestressed concrete box girder joint;since the width of the box girder is larger than the width of the column,it is necessary to add a column cap in the joint area,so as to ensure that the force borne by the girder part(generally the box girder web)that the width is more than the width of column is smoothly transferred to the column by the column cap.Therefore,the longitudinal steel bars and prestressed steel bars in the girder web can pass through the two sides of the steel tube(steel)in the joint area,which not only avoids the collision with the steel tube(steel)in the joint area,but also helps to ensure the accuracy of linear shape of the prestressed steel bars.The practice that the joint area is added a column cap needs to be verified the reliability of force transmission,so it is necessary to investigate the seismic performance of the designed joints.In this paper,based on the beam-column joints of the track bearing layer of a real high-speed railway station building,four concrete filled steel tubular(steel reinforced concrete)column-prestressed concrete box girder joints are designed with a 1 / 8 scale,including SJ1,SJ2 and SJ3 which are strong joints and WJ which is weak joint;SJ1 is the interior joint specimen of concrete filled steel tubular column with the same height and span of left and right beams,SJ2 is the interior joint of concrete filled steel tubular column with different height and span of left and right beams,SJ3 is the exterior joint of steel reinforced concrete column,and WJ is the interior joint of concrete-encased concrete filled steel tubular column with the same height and span of left and right beams.The seismic performance of the four joints is investigated by the experiment,finite element simulation and theoretical analysis.The main achievements of this paper are as follows :1.Low cyclic loading tests were carried out on four concrete filled steel tubular(steel reinforced concrete)column-prestressed concrete box girder joints.The constant axial load was applied on the top of the column and the beam end was subjected to reciprocating loading.The test results show that the bending failure of beam bottom occurs in specimen SJ1 which is accompanied by shear failure in the joint area,the tensile failure of steel tube of upper column occurs in specimen SJ2,the compressive and bending failure of upper column concrete occurs in specimen SJ3,and the shear failure of joint core area occurs in specimen WJ.According to the experimental data,the hysteresis curve,skeleton curve,strength and stiffness degradation law,ductility performance and energy dissipation capacity of four joint specimens are analyzed and studied.The results indicate that except SJ2,there is a certain pinch phenomenon in the hysteretic curves of the other three joints.The ductility of the three strong-joint specimens is good,while that of the weakjoint specimen is relatively poor.Except the equivalent viscous damping coefficient of the specimen SJ3 is relatively small,the equivalent viscous damping coefficients of the other three joints are more than 0.15,which shows good energy dissipation capacity.Compared with the longitudinal steel bars in the box girder flange,the longitudinal steel bars in the box girder web show stress hysteresis phenomenon.2.The finite element analysis models of four joint specimens under cyclic loading were established.Considering the constraint effect of steel tube on concrete,different constitutive models were used for finite element simulation of concrete inside and outside steel tube.Concrete Damage Plasticity model was adopted for concrete and tensile and compressive damage factors were introduced to consider the performance of concrete under cyclic loading;the appropriate element type was selected according to the characteristics of each component,and the components were partitioned in order to get good meshes.The interaction between steel tube and concrete was considered in the finite element analysis models.The finite element simulation results are in good agreement with the experimental results.The finite element analysis models were further used to analyze the force mechanism of each component of the four joint specimens at the characteristic point.3.Taking the weak joint specimen WJ as the prototype,the parametric modeling analysis of various components affecting the shear bearing capacity of concrete-encased concrete-filled steel tubular column joints was carried out by ABAQUS.The specific parameters included the axial compression ratio of the joint core area,the strength of the concrete in the steel tube,the strength of the steel tube,the steel ratio of the section and the degree of prestress.By analyzing the force mechanism of concrete-encased concrete-filled steel tubular column joints,the shear bearing capacity formula of the joint core area was proposed by using the superposition principle,and compared with the shear force of the finite element models when the joint core area was destroyed under different parameters.The results show good agreement,indicating that the shear bearing capacity formula of the joint core area is correct and applicable.